Adjustable reflector sight for hightrajectory projectiles



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United States Patent 3 339,450 ADJUSTABLE REFLECTOR SIGHT FOR HIGH-TRAJECTORY PROJECTILES Frederick P. Reed, Ludlow, Mass., assignor to theUnited States of America as represented by the Secretary of the ArmyFiled Aug. 1, 1963, Ser. No. 299,439 4 Claims. (Cl. 88-1) The inventiondescribed herein may be manufactured and used by or for the Governmentfor governmental purposes without the payment to me of any royaltythereon.

This invention relates to sights for guns and more particulanly to areflector sight to be used with shoulder-supported firearms forhigh-trajectory projectiles.

Included in the arsenal of modern weapons are shoulder-supportedfirearms which discharge grenades at a low velocity and with a hightrajectory so that, when the target is some distance from the shooter,the firearm has to be elevated to a considerable angle for lobbing thegrenade to the target. Considerable difiiculty has been encountered inproviding a suitable sighting device for such firearms because theconsiderable angle of elevation requires that the conventional type ofrear sight mounted on top of the barrel be adjustable up to aconsiderable height and, therefore, is bulky and inconvenient to use.Attempts have been made to overcome these problems by designing sightingdevices which are mounted on one side of the weapon but these are notsatisfactory as they are not interchangeable for right-hand andleft-hand shooters. Also, sighting along a line different from that ofthe barrel is not satisfactory.

Moreover, the barrels of such high-trajectory grenade launching firearmsare rifled to spin the grenade during travel down the barrel and,because of the low velocity of the grenade, this spin causes it to driftaway from the target with the amount of drift increasing with theincrease in the distance of the target. Previous sighting devices havenot successfully solved the problem of automatically compensating forthis drift.

It is, therefore, one object of this invention to provide for suchfirearms a reflector sighting device which utilizes an adjustable mirrorfor range finding and for automatically compensating for the knowncomponents of drift at the different range settings.

It is a further object of this invention to provide such a sightingdevice which is compact in size, rugged in construction and easy to use.

The specific nature of the invention as well as other objects andadvantages thereof will clearly appear from a description of a preferredembodiment as shown in the accompanying drawings in which:

FIG. 1 is an elevational view of a grenade launcher with the sightingdevice of this invention mounted thereon;

FIG. 2 is an enlarged view taken along line 22 of FIG. 1;

FIG. 3 is a view taken along line 33 of FIG. 2 and shows the position ofthe adjustable mirror when adjusted for zero range;

FIG. 4 is a view similar to FIG. 3 but shows the position of theadjustable mirror, and the angle of elevation of the grenade launcher,when the sighting device is adjusted for the maximum 375-yard range;

FIG. 5 is a view taken along line 5-5 of FIG. 3;

FIG. 6 is a view taken along line 6-6 of FIG. 3;

FIG. 7 is a view taken along line 7-7 of FIG. 4;

FIG. 8 is a view taken along line 88 of FIG. 4;

FIG. 9 is a view taken along line 99 of FIG. 1;

FIG. 10 is a fragmentary perspective view of the front end of the shaftin the knob assembly to show the helically formed cam surface;

3,339,450 Patented Sept. 5, 1967 FIG. 11 is a schematic 'view showing,exaggerated, the relationship between the sight line and the bore axisof the firearm in the horizontal plane, with the drift of the grenadebeing compensated for at the -yard range adjustment;

FIG. 11a is a schematic view showing the relationship of the sight lineand the optical path in the sighting device respective to the line axisof the firearm when the sighting device is adjusted to the IOO-yardrange setting;

FIG. 12 is a view similar to FIG. 11a but shows the relationship of thesight line and bore axis when the sighting device is adjusted for the250-yard range;

FIG. 12a is a view similar to FIG. 11a but shows the relationship of thesight line and the optical path respective to the bore axis when thesighting device is adjusted for the 250-yard range;

FIG. 13 is a view similar to FIGS. 11a and 12a but shows therelationship of the sight line and bore axis when the sighting device isadjusted for the 375-yard range; and

FIG. 13a is a view similar to FIGS. 11a and 12a but shows therelationship of the sight line and optical parts respective to the boreaxis when the sighting device is adjusted for the 375-yard range.

Shown in the figures is a grenade launcher 12, such as the M79 GrenadeLauncher, which is shoulder-supported for firing. Grenade launcher 12includes a barrel 14 which is rifled to spin a grenade (not shown)during discharge therealong and which has a bore axis xx. A sightingdevice 16, mounted on barrel 14 by means of front bracket 18 and a rearbracket 20, includes a tube 22, an eyepiece 24 of approximatelytwo-power magnification mounted on the rear end of the tube and anoptical adjuster 26 with a mirror arrangement 27 mounted on the frontend. Sighting device 16 is mounted on barrel 14 so that the front end ofoptical adjuster 26 is adjacent the muzzle end of the barrel, wherebythe front end of the barrel will not block the front of the opticaladjuster when sighting at a distant target when the elevation of grenadelauncher 12 is consequently very high. Optical adjuster 26 includes ahousing 28 of substantially rectangular configuration with a sleeveextending integrally rearward from the lower portion of the rear endthereof for receiving the front end of tube 22. Extending longitudinallythrough the upper portion of housing 28 is a stepped bore 32 which isinterrupted by a clearance 34 which provides communication between thebore and a chamber 36 extending rearwardly into the housing from thefront end thereof.

Adjuster assembly 38 includes a knob 40 disposed outside of bore 32 formanual turning and a shaft 42 which is slidingly and rotatingly receivedby the bore. Knob 43 is provided with a pintle 44 having an annularchannel 46 which receives a pin 48 mounted laterally through housing 28for holding knob 40 against axial displacement while permitting rotationthereof. A threaded hole 49 extends into pintle 44 from the front endthereof and is arranged to receive a matingly threaded portion 50 formedon the rear end of shaft 42, whereby rotation of knob 40 is converted totranslational displacement of shaft 42 when the knob is rotated and theshaft is held against rotation respective thereto. The front end ofshaft 42 is slabbed to form a curved cam surface 52 having apredetermined helix which will be further explained hereinafter. A pin54 extends laterally through housing 28 so as to have sliding contactwith surface 52, whereby, when knob 40 is turned and shaft 42 is movedlongitudinally, a limited and predetermined angular displacement of theshaft around its longitudinal axis is effected. This angulardisplacement of shaft 42 is utilized to adjust the sight line ofsighting device 16 laterally as will be explained hereinafter.

A pin 56 extends laterally through shaft 42 and projects from oppositesides thereof to form end portions 58 which pivotally support a firstmirror 6t) in mirror arrangement 27. First mirror 66 is essentiallyrectangular in configuration with a reflecting surface 62 on the frontface and is provided with an integral pair of hangers 64 which extendrearwardly from the top rear portion of the first mirror. Hangers 64 areeach provided with a hole for receiving one of the ends 53 and, as isbest shown in FIGS. 3 and 4, the hangers are also respectively providedwith a planar side 66 and an arcuate corner 63 formed where each of suchplanar sides join the front face of first mirror 64 Corners 68 havesliding and pivotal contact with a front side 7!) of clearance 34 sothat, when shaft 42 is forwardly displaced by knob 49, front mirror 60is pivoted upwardly. Corners 68 are resiliently held in contact withfront side 7% by a double coil spring '72 which is supported by a pin 74mounted laterally through the hangers 64. Proper clearance is providedbetween the sides of first mirror 66 and the sides of housing 28 topermit sufiicient lateral displacement of the first mirror for thelateral adjustment of the sight line as hereinafter described.

Reflecting surface 62 is positioned directly rearward of an aperture 76formed in the front end of housing 28 above a second mirror 78, inmirror arrangement 27, fixedly mounted in the housing. Second mirror 78is located immediately in front of tube 22 so that a reflecting surface80 on the second mirror faces the end of its tube and is disposed at a45 angle relative to the center axis thereof to reflect the imagetransmitted thereto by first mirror 64 to eyepiece 24 along optical pathz-z of sighting device 16.

The operation of sighting device 16 can best be understoOd by firstreferring to FIG. 3 wherein it is seen that, when reflecting surfaces 62and iii) are parallel, a sight line yy, which is the forward projectionof optical path zz, is parallel with the portion of the optical pathwithin tube 22. Therefore, as the axis of tube 22 and bore axis xx areparallel, sighting device 16 is adjusted for zero range.

Now, referring to FIGS. 11a, 12a, and 13a, it is seen that, when firstmirror 6t) is tilted about lateral pin 56 by the longitudinaldisplacement of shaft 42 through rotation of knob 40 the angle ofreflection b, which is determined by the angular relationship ofreflection surface 62 respective to optical path z-z, is decreased,angle of incidence a is similarly decreased and sight line yy isconsequently inclined downwardly relative to bore axis xx. Therefore, inorder to bring sight line yy back onto a target 52 so that the imagethereof will be transmitted to eyepiece 24-, the elevation of grenadelauncher 12 must be raised.

Provided on knob 40 are range distance markings 84 which are calibratedso that, when a selected one of the markings is properly indexed, theangular position of first mirror 6:? is adjusted to correctly elevategrenade launcher 12 for the range distance when sight line y-y is ontarget 82. Provided in eyepiece 24 are cross-hairs S6 for increasing theaccuracy of sighting device 16 and the eyepiece is provided with a lowmagnification to improve the sight picture. Grenade launcher 12 iselevated 38, when aimed at target 82, which is 375 yards distant, butbecause a one degree change in the angular displacement of first mirrorchanges the inclination of sight line yy 2 with the angle of inclinationa and the angle of reflection 12 being similarly effected, the angularchange of first mirror is only 19. Thus, it is evident that sightingdevice 16 is compact with very little displacement required of themoving parts thereof.

As has been noted hereinbefore, the rotation of knob 40 displaces shaft42 longitudinally and, through the sliding cooperation of surface 52with pin 54, the longitudinal displacement effects an angulardisplacement of the shaft about its longitudinal axis and as firstmirror 60 depends therefrom the angular displacement of the shaft swingsthe first mirror laterally according to the helical angle of thesurface. As the angular relationship of first mirror 60 respective tothe axis of shaft 42 is less than 90 and as the first mirror isdisplaced in an arcuate path when shaft 42 is angularly displaced thefirst mirror is tilted respective to reflecting surface of second mirror73 to shift sight line y-y laterally. The helix of surface 52 isgenerated so that, when shaft 42 is positioned for correctly displacingfirst mirror 60 to the range distances, the shaft is angularly displacedto swing the first mirror laterally and thereby tilt it respective tosecond mirror 78 so as to change angle of incidence a laterally andshift sight line yy accordingly to correct the known component ofgrenade drift at the indexed range distances. The relationship betweenthe elevation adjustment and drift compensation of sighting device 16 isgraphically illustrated in FIGS. 11 through 130. A windage adjustment 88is provided in rear bracket 20 for pivoting sighting device 16 laterallyaround a ball joint in front bracket 18.

Although a particular embodiment of the invention has been described indetail herein, it is evident that many variations may be devised withinthe spirit and scope thereof and the following claims are intended toinclude such variations.

I claim:

1. For shoulder-supported firearms firing high-trajectory projectileswith a predetermined component of lateral drift: a sighting deviceincluding a tube mounted on a barrel of the firearm so as to be paralleltherewith, an eyepiece mounted on the rear end of said tube, and anoptical adjuster mounted on the front end of said tube; said opticaladjuster including a housing, a pair of mirrors respectively mounted insaid housing so as to be vertically inclined respective to the axis ofsaid tube and substantially in parallel relationship and so as tocooperate in effecting an adjustable sight line extending from anoptical path determined by said eyepiece and said pair of mirrors, saidpair of mirrors including a first mirror and a second mirror, saidsecond mirror being fixedly mounted in said housing for reflecting animage transmitted thereto by said first mirror to said eyepiece; anadjuster assembly including a rotatable knob, sight line adjusting meansoperationally disposed between said knob and said first mirror includinga shaft mounted in said housing for longitudinal and angulardisplacement, cooperating thread means on said knob and said shaft forconverting rota tional displacement of said knob to longitudinaldisplacement of said shaft, a pin mounted laterally through said shaftfor mounting said first mirror thereto for pivotal displacementrespective thereto and for lateral swinging displacement therewith,abutting portions on said first mirror and said housing arranged incooperation to convert longitudinal displacement of said shaft topivotal displacement of said first mirror about said pin for elevationaladjustment of the sight line to selected range distances, and cam meanson said shaft cooperating with fixed means in said housing forconverting longitudinal displacement of said shaft to angulardisplacement thereof to swing said first mirror laterally in an arcuatepath while being pivotally displaced for elevational adjustment of thesight line to also adjust the sight line laterally.

2. The sighting device as defined in claim 1, wherein said fixed meansis a pin mounted through said housing, and said cam means is a curvedcam surface formed on said shaft for sliding contact with said pin.

3. The sighting device as defined in claim 1, wherein said cam means isa curved cam surface formed with a predetermined helix for displacingsaid first mirror to adjust the sight line laterally to compensate forthe predetermined component of lateral drift of the projectiles at theselected range settings.

5 4. The sighting device as defined in claim 1, wherein said secondmirror is mounted at a 45 angle to the axis of said tube.

References Cited UNITED STATES PATENTS 6 2,627,779 2/1953 Szelwach88-2.4 3,145,248 8/1964 Shuping 882.4 X

DAVID H. RUBIN, Primary Examiner. 5 JEWELL H. PEDERSEN, Examiner.

T. KUSMER, Assistant Examiner.

1. FOR SHOULDER-SUPPORTED FIREARMS FIRING HIGH-TRAJECTORY PROJECTILES WITH A PREDETERMINED COMPONENT OF LATERAL DRIFT: A SIGHTING DEVICE INCLUDING A TUBE MOUNTED ON A BARREL OF THE FIREARM SO AS TO BE PARALLEL THEREWITH, AN EYEPIECE MOUNTED ON THE REAR END OF SAID TUBE, AND AN OPTICAL ADJUSTER MOUNTED ON THE FRONT END OF SAID TUBE; SAID OPTICAL ADJUSTER INCLUDING A HOUSING, A PAIR OF MIRRORS RESPECTIVELY MOUNTED IN SAID HOUSING SO AS TO BE VERTICALLY INCLINED RESPECTIVE TO THE AXIS OF SAID TUBE AND SUBSTANTIALLY IN A PARALLEL RELATIONSHIP AND SO AS TO COOPERATE IN EFFECTING AN ADJUSTABLE SIGHT LINE EXTENDING FROM AN OPTICAL PATH DETERMINED BY SAID EYEPIECES AND SAID PAIR OF MIRRORS, SAID PAIR OF MIRRORS INCLUDING A FIRST MIRROR AND A SECOND MIRRORS, SAID SECOND MIRROR BEING FIXEDLY MOUNTED IN SAID HOUSING FOR REFLECTING AN IMAGE TRANSMITTED THERETO BY SAID FIRST MIRROR TO SAID EYEPIECE; AN ADJUSTER ASSEMBLY INCLUDING A ROTATABLE KNOB, SIGHT LINE ADJUSTING MEANS OPERATIONALLY DISPOSED BETWEEN SAID KNOB AND SAID FIRST MIRROR INCLUDING A SHAFT MOUNTED IN SAID HOUSING FOR LONGITUDINAL AND ANGULAR DISPLACEMENT, COOPERATING THREAD MEANS ON SAID KNOB AND SAID SHAFT FOR CONVERTING ROTATIONAL DISPLACEMENT OF SAID KNOB TO LONGITUDINAL DISPLACEMENT OF SAID SHAFT, A PIN MOUNTED LATERALLY THROUGH SAID SHAFT FOR MOUNTING SAID FIRST MIRROR THERETO FOR PIVOTAL DISPLACEMENT RESPECTIVE THERETO AND FOR LATERAL SWINGING DISPLACEMENT THEREWITH, ABUTTING PORTIONS ON SAID FIRST MIRROR AND SAID HOUSING ARRANGED IN COOPERATION TO CONVERT LONGITUDINAL DISPLACEMENT OF SAID SHAFT TO PIVOTAL DISPLACEMENT OF SAID FIRST MIRROR ABOUT SAID PIN FOR ELEVATIONAL ADJUSTMENT OF THE SIGHT LINE SELECTED RANGE DISTANCES, AND CAM MEANS ON SAID SHAFT COOPERATING WITH FIXED MEANS IN SAID HOUSING FOR CONVERTING LONGITUDINAL DISPLACEMENT OF SAID SHAFT TO ANGULAR DISPLACEMENT THEREOF TO SWING SAID FIRST MIRROR LATERALLY IN AN ARCUTAE PATH WHILE BEING PIVOTALLY DISPLACED FOR ELEVATIONAL ADJUSTMENT OF THE SIGHT LINE TO ALSO ADJUST THE SIGHT LINE LATERALLY. 